1. Field of the Invention
The present invention relates to an illumination optics and an image projecting apparatus having thereof. The invention relates to, for example, the illumination optics which is used for a projector and synthesizes light fluxes emitted from two lamps so as to supply the synthesized light flux to a light modulating device, and the image projecting apparatus having thereof.
2. Description of the Related Art
Presently, high brightness is required in projectors, particularly, data projectors. Lamps, which are currently supplied and have short arc length, have good system efficiency, but their output is limited. For this reason, in a system (image projecting apparatus) which use only one lamp, its output as a system is limited, and heightening of its brightness is limited. Meanwhile, lamps having high output have a short life, and require frequent maintenance such as lamp exchange in the market. As optics of lamps for projectors, therefore, illumination optics which use two lamps whose output is limited as independent lamp so as to obtain large output are now the mainstream.
Such an illumination optics is disclosed in, for example, U.S. Pat. No. 6,505,939 (hereinafter, US' 939). The illumination optics in US' 939 synthesizes light beams from two light sources using an integrator rod and supplies the synthesized light beam to a light modulating device via a color wheel. When the integrator rod is used, the light whose illuminance distribution is made to be uniform can be supplied to the light modulating device via the color wheel.
On the other hand, an illumination optics which uses a plurality of lamps but does not use an integrator rod is disclosed in, for example, U.S. Pat. No. 6,666,558 (US' 558). In the illumination optics in US' 558, light sources and light condensing devices are arranged so that condensing positions of light beams emitted from the respective light sources are superposed on each other on a color wheel or its vicinity by the light condensing devices (for example, elliptical mirrors) corresponding to the light sources. As a result, the size of a light source image which is formed on the color wheel or its vicinity is suppressed to minimum, and thus enlargement of the color wheel and image deterioration due to color mixing are avoided.
Like US' 939, however, when the color wheel is arranged on the light emission side of the integrator rod, a light emission surface of the integrator rod and a modulation surface of the light modulating device are approximately optically-conjugated. For this reason, when boundary portions of respective color filters of the color wheel cross the light emission surface of the integrator rod, color information of the light passing through the respective color filters cutting across the boundary portions is reflected directly onto the modulation surface. As a result, color shading partially occurs on the modulation surface, the quality of the image to be projected onto a screen via the light modulating device is deteriorated. When the boundary portions of the respective color filters cross the light emission surface of the integrator rod, switching of the light modulating device into an OFF state causes deterioration in light utilization efficiency (brightness), and thus the switching is not appropriate. In order to avoid the above inconvenience, therefore, it is desirable that the color wheel is arranged on the light incident side of the integrator rod.
Like US' 558, however, when the light condensing positions of the light beams emitted from the light sources are superposed on each other on the color wheel or its vicinity by the light condensing devices corresponding to the light sources, considerable heat energy is generated on the light condensing position. The respective color filters of the color wheel are formed by, for example, dielectric films, and thus their heat resistance is inferior. For this reason, when the considerable heat energy is generated concentratedly one point of the color wheel or its vicinity, the property of the color wheel is deteriorated or changed. Like US' 558, therefore, when the light condensing positions of the emitted light beams from the light sources are superposed on each other on the color wheel or its vicinity, the arrangement of the color wheel on the light incident side of the integrator rod is prevented.